Acid grassland, Scotland • © NERC Semi-Natural Grasslands ...€¦ · Countryside Survey: UK Results from 2007 CHAPTER 4 • Semi-Natural Grasslands: Neutral, Calcareous and Acid

Countryside Survey: UK Results from 2007 CHAPTER 4 • Semi-Natural Grasslands: Neutral, Calcareous and Acid Grassland Broad Habitats

4. Semi-Natural Grasslands: Neutral, Calcareous and Acid Grassland Broad Habitats

� Acid grassland, Scotland • © NERC

Summary

• The area of Neutral Grassland increased by 6.0% and the area of Acid Grassland increased by 5.5% in the UK between 1998 and 2007; the area of Calcareous Grassland did not change between these dates.

• Plant species richness was unchanged in Neutral Grassland but decreased in areas of Neutral Grassland targeted in Countryside Survey for their botanical interest in Great Britain between 1998 and 2007.

• Competitive and stress tolerating plant species increased at the expense of species of open ground in Neutral Grassland in Great Britain between 1998 and 2007.

• Plant species preferring fertile soils with high pH decreased while species preferring wetter conditions and/or prefer shadier conditions increased in Neutral Grassland in Great Britain between 1998 and 2007.

• The vegetation characteristics of Calcareous Grassland changed little in Great Britain between 1998 and 2007.

• Plant species richness decreased in Acid Grassland in Great Britain between 1998 and 2007.

• Competitive plant species and plant species preferring wetter conditions increased, while species of open ground decreased in Acid Grassland in Great Britain between 1998 and 2007.

• The mean pH of Neutral Grassland soils (0-15cm) increased in Great Britain between 1998 and 2007, but the mean pH of Acid Grassland soils (0-15cm) did not change signifi cantly in Great Britain between 1998 and 2007.

• There was no detectable change in the mean carbon concentration in Neutral Grassland soils (0-15cm) in Great Britain between 1998 and 2007, but in Acid Grassland soils (0-15cm) there was a signifi cant decrease in Great Britain during the same period.

38


4.1 Introduction1

While the most productive grasslands in the UK fall into the Improved Grassland Broad Habitat (19% of Great Britain’s land area), large areas of semi-improved grassland still exist and these have been traditionally managed for livestock grazing and/or hay. They make a large contribution to national dairy, beef and lamb production and now tend to be associated with smaller farms and high quality produce or small areas on larger farms where intensifi cation has been impractical for physical or fi nancial reasons. Typically, these grasslands have been in existence for many decades or centuries and those examples with the highest conservation value have not been agriculturally improved by ploughing, re-seeding or the use of inorganic fertilisers. A large majority of these grasslands are now protected either as nature reserves, SSSIs or are under sympathetic management in agri-environment schemes.

These measures have been aimed at achieving the favourable condition of the best examples of these semi-natural grasslands; and maintaining or restoring other grasslands.

Small areas of semi-natural grassland (typically less than 0.5ha) are too small to attract protection or designation and may often be diffi cult to manage, yet will have been sampled by Countryside Survey (CS) plots. Although of lower conservation value than larger blocks of semi-natural habitat, these small areas are especially vulnerable to intensive land-use pressures. Conversely, the small areas are also susceptible to lack of management leading to succession to tall grassland, scrub and ultimately woodland. The changes in semi-natural grassland reported here derive from a random sample of the countryside and are therefore more representative of the Broad Habitats in the wider countryside rather than the often larger (but proportionally fewer) blocks of semi-natural habitat found on designated sites.

The three Broad Habitats included in this chapter are characteristic of soils with diff ering pH values. Neutral Grassland occurs on soils that are neither strongly acid nor lime-rich (pH 5.5-6.5); Calcareous Grassland occurs on lime rich soils (pH>6.5); and Acid Grassland occurs on acid soils (pH<5.5). Much of the Acid Grassland in Great Britain occurs in the uplands and so reference is also made to this Broad Habitat in Chapter 7. More narrowly defi ned BAP Priority Habitats occur within each of these Broad Habitats and CS data may contribute to their assessment.

4.2 Area of semi-natural grasslands

• The area of Neutral Grassland increased by 6.0% and the area of Acid Grassland increased by 5.5% in the UK between 1998 and 2007; the area of Calcareous Grassland did not change.

4.2.1 Neutral Grassland

The area of Neutral Grassland was estimated to cover approximately 2.4 million ha in 2007 or 10% of the UK (Table 4.1). A 6% increase from 1998. This followed a 20% increase between 1990 and 1998 (Fig. 4.1). In contrast, there was a signifi cant 12.5% decrease in Neutral Grassland in Northern Ireland between 1998 and 2007.

4.2.2 Calcareous Grassland

The area of Calcareous Grassland was estimated to cover approximately 59,000 ha in 2007 or approximately 0.2% of the UK (Table 4.1). The small sample size makes it diffi cult to detect small changes in the area of this Broad Habitat and none were detected in the UK or Great Britain between 1998 and 2007, although there was a signifi cant decrease in Great Britain between 1990 and 1998 (Table 4.2, Fig. 4.2).

� Figure 4.2: Change in the area of Calcareous Grassland across Great Britain between 1990 and 2007. Signifi cant changes (* p<0.05) are shown between the dates bracketed. 95% CI are shown for each data point.

0

20

40

60

80

100

120

140

Are

a (’

00

0s

ha)

*

1990 1998 2007

1 Note: For further information on the Broad Habitat classifi cation, vegetation Aggregate Classes or ACs, sampling plots and other Countryside Survey terminology see Chapter 1 (Methodology).

� Figure 4.1: Change in the area of Neutral Grassland across Great Britain between 1990 and 2007. Signifi cant changes (* p<0.05, ** p<0.01) are shown between the dates bracketed. 95% CI are shown for each data point.

0

500

1000

1500

2000

2500

3000

Are

a ('

00

0s

ha)

***

1990 1998 2007

39


4.2.3 Acid Grassland

The area of Acid Grassland was estimated to cover approximately 1.6 million ha in 2007 or approximately 6.5% of the UK (Table 4.3). In Great Britain the area of Acid Grassland increased by 5.7% between 1998 and 2007. This followed a larger decrease of 17.5% between 1990 and 1998. Overall there was a 12.7% decrease between 1990 and 2007 (Table 4.3, Fig. 4.3).

� Figure 4.3: Change in the area of Acid Grassland across Great Britain between 1990 and 2007. Signifi cant changes (** p<0.01) are shown between the dates bracketed. 95% CI are shown for each data point.

0

500

1000

1500

2000

2500

Are

a ('

00

0s

ha)

****

1990 1998 2007

� Table 4.2: Estimates of the area (‘000s ha) and percentage of land area of Calcareous Grassland in the UK from 1998 to 2007 and Great Britain from 1984 to 2007 are shown. Arrows denote signifi cant change (p<0.05) in the direction shown. Note that because of changes in defi nitions that have been applied retrospectively, the estimates from 1990 and more especially 1984 are not in all cases directly comparable with later surveys. Data not available = na.

1984 1990 1998 2007 Direction of signifi cant changes

1998-2007Area

(‘000s ha)%

Area (‘000s ha)

%Area

(‘000s ha)%

Area (‘000s ha)

%

GB 75 0.3 78 0.3 61 0.3 57 0.2

England na na 42 0.3 33 0.2 30 0.2

Scotland na na 36 0.4 28 0.4 26 0.3

Wales na na 1 0.1 1 0.1 1 0.1

Northern Ireland na na na na 2 0.1 2 0.1

UK na na na na 63 0.3 59 0.2

� Table 4.1: Estimates of the area (‘000s ha) and percentage of land area of Neutral Grassland in the UK from 1998 to 2007 and Great Britain from 1984 to 2007 are shown. Arrows denote signifi cant change (p<0.05) in the direction shown. Note that because of changes in defi nitions that have been applied retrospectively, the estimates from 1990 and more especially 1984 are not in all cases directly comparable with later surveys. Data not available = na.


1998-2007Area

(‘000s ha)%

Area (‘000s ha)

%Area

(‘000s ha)%

Area (‘000s ha)

%

GB 467 2.0 1669 7.2 2007 8.6 2176 9.3 ~England na na 994 7.5 1290 9.8 1453 11.0 ~

Scotland na na 428 5.4 430 5.4 461 5.8

Wales na na 247 11.7 287 13.5 263 12.4

Northern Ireland na na na na 264 18.6 231 16.3 !

UK na na na na 2271 9.2 2407 9.7

� Neutral grass with anthills, England • © Peter Stroh

40


The introduction of new recording categories for Broad Habitats in 1998 may have aff ected the estimates of changes between 1990 and 1998 in Neutral and Acid Grassland. The change estimates between 1998 and 2007 are more reliable because the same codes were used in both surveys.

4.3 Changes between the semi-natural grassland habitats

Most Neutral Grassland remained as that Broad Habitat between 1998 and 2007. There were conversions to and from Improved Grassland which virtually cancelled each other out and more Arable and Horticulture Broad Habitat became Neutral Grassland than the reverse. This pattern is consistent with the substantial increase in set-aside during the period. The pattern was also confi rmed by an investigation of the conversions based on the primary mapping codes recorded by surveyors, which indicated a net shift from arable crops to semi-improved neutral grassland and tall neutral grassland. A small amount of Coniferous Woodland became Neutral Grassland after felling and a similar amount of Neutral Grassland became Broadleaved, Mixed and Yew Woodland (Annex 6, www.countrysidesurvey.org.uk).

There were very few changes in the conversions to and from Calcareous Grassland Broad Habitat between 1998 and 2007. There were small conversions to and from Neutral Grassland but little else (Annex 6).

There were small conversions from the Broad Habitats: Bog; Fen, Marsh and Swamp; Bracken; and Coniferous Woodland to Acid Grassland, and a small fl ow from Acid Grassland to Dwarf Shrub Heath, between 1998 and 2007 (Annex 6).

4.4 Condition of semi-natural grasslands

4.4.1 Changes in the Neutral Grassland Broad Habitat

• Plant species richness was unchanged in Neutral Grassland but decreased in areas of Neutral Grassland targeted in CS for their botanical interest in Great Britain between 1998 and 2007.

• Competitive and stress tolerating plant species increased at the expense of species of open ground in Neutral Grassland in Great Britain between 1998 and 2007.

• Plant species preferring fertile soils with high pH decreased while species preferring wetter conditions and/or prefer shadier conditions increased in Neutral Grassland in Great Britain between 1998 and 2007.

� Table 4.3: Estimates of the area (‘000s ha) and percentage of land area of Acid Grassland in the UK from 1998 to 2007 and Great Britain from 1984 to 2007 are shown. Arrows denote signifi cant change (p<0.05) in the direction shown. Note that because of changes in defi nitions that have been applied retrospectively, the estimates from 1990 and more especially 1984 are not in all cases directly comparable with later surveys. Data not available = na.


1998-2007Area

(‘000s ha)%

Area (‘000s ha)

%Area

(‘000s ha)%

Area (‘000s ha)

%

GB 1476 6.3 1821 7.8 1502 6.4 1589 6.8 ~

England na na 475 3.6 400 3.0 396 3.0

Scotland na na 1095 13.6 911 11.4 983 12.3 ~Wales na na 256 12.1 191 9.0 211 9.9

Northern Ireland na na na na 13 0.9 10 0.7

UK na na na na 1516 6.1 1599 6.5

� Semi-natural grassland, England • © Sue Wallis

41


Species richness: While there was no change in plant species richness in Main Plots across Great Britain (Table 4.4), a decrease was recorded in Scotland. In areas targeted in CS for their botanical interest, plant species richness decreased from 14.3 to 12.9 species per plot in Great Britain between 1998 and 2007, following a similar decrease between 1990 and 1998 (Table 4.5, Fig. 4.4). The Targeted Plots may have been located in small patches of Priority Habitat within larger Neutral Grassland areas or within patches of other habitats such as scrub. The increase in the ratio of grasses to forbs between 1990 and 1998 and the subsequent decrease between 1998 and 2007 requires further investigation.

The decrease in both the number of plant species used by farmland birds as food (6.6 in 1990 to 5.6 in 2007) (Fig. 4.5) and those used by butterfl y caterpillars as food (6.9 in 1990 to 5.9 in 2007) (Fig. 4.6) in Neutral Grassland Targeted Plots between 1990 and 2007 shows that these refuges have not just deteriorated for plants but possibly for animals too (Table 4.5).

Other Characteristics of the vegetation of Neutral Grassland: The signifi cant increase of competitive species at the expense of ruderal species in Main Plots (Table 4.4) and Targeted Plots (Table 4.5), along with the signifi cant decrease in the mean Light Score (Tables 4.4 and 4.5) show that Neutral Grasslands became more densely vegetated and more shaded across

� Table 4.5: Change in the characteristics of vegetation in 2m x 2m Targeted Plots in the Neutral Grassland Broad Habitat across Great Britain between 1990 and 2007. Mean values for 1998 and 2007 are presented; those for 1990 are available in Annex 7. Arrows denote signifi cant change (p<0.05) in the direction shown. Analyses are described in Box 1.3.

Mean values

(GB)

Direction of signifi cant changes

1998 – 2007


1990 - 1998


1990 - 2007

Vegetation Condition Measures 1998 2007 GB E S W GB E S W GB E S W

Species Richness (No. of Species) 14.3 12.9 ! ! ! ! ! ! ! ~ ! ! !

No. of Bird Food Species 6.2 5.6 ! ! ! ! ! ! ~ ! ! !

No. of Butterfl y Food Species 6.4 5.9 ! ! ! ! ! ! ! ! !

Grass:Forb Ratio 0.86 0.67 ! ~ ~

Competitor Score 2.98 3.04 ~ ~ ~ ~ ~ ~ ~ ~

Stress Tolerator Score 2.23 2.23

Ruderal Score 2.6 2.55 ! ! ! ! ! !

Light Score 6.91 6.86 ! ! ! !

Fertility Score 5.17 5.26 ~ ~ ~ ~ ~

Ellenberg pH Score 5.87 5.91 ~ !

Moisture Score 5.74 5.76 !

� Table 4.4: Change in the characteristics of vegetation in 200m2 Main Plots in the Neutral Grassland Broad Habitat across Great Britain between 1990 and 2007. Mean values for 1998 and 2007 are presented; those for 1990 are available in Annex 7. Arrows denote signifi cant change (p<0.05) in the direction shown. Analyses are described in Box 1.3.

Mean values

(GB)


1998 – 2007


1990 - 1998


1990 - 2007


Species Richness (No. of Species) 21.2 20.4 ! !

No. of Bird Food Species 10.6 10.4 !

No. of Butterfl y Food Species 9.9 9.7 !

Grass:Forb Ratio 1.10 1.10 ~

Competitor Score 2.75 2.81 ~ ~ ~

Stress Tolerator Score 2.19 2.23 ~ ~

Ruderal Score 2.95 2.87 ! ! ! ! ! !

Light Score 7.01 6.98 ! ! ~

Fertility Score 5.16 5.10 ! ! !

Ellenberg pH Score 5.86 5.80 ! ! ! !

Moisture Score 5.45 5.52 ~ ~ ~ ~ ~

42


� Table 4.6: The 10 plant species with the largest increase and decrease in frequency in Main Plots in the Neutral Grassland Broad Habitat across Great Britain between 1998 and 2007.

Species with increasing frequency Change Index Species with decreasing frequency Change Index

Glyceria fl uitans Floating Sweet-grass 0.37 Phleum pratense sens. lat. Timothy -0.45

Juncus eff usus Soft Rush 0.32 Poa annua Annual Meadow-grass -0.33

Ranunculus bulbosus Bulbous Rush 0.29 Leontodon autumnalis Autumn Hawkbit -0.32

Ranunculus acris Meadow Buttercup 0.27 Cirsium vulgare Spear Thistle -0.29

Cirsium palustre Marsh Thistle 0.27 Poa pratensis sens. lat. Smooth Meadow-grass -0.26

Holcus lanatus Yorkshire Fog 0.25 Convolvulus arvensis Field Bindweed -0.25

Vicia sativa Common Vetch 0.24 Anagallis arvensis Scarlet Pimpernell -0.24

Rubus fruticosus agg. Bramble 0.23 Alopecurus geniculatus Marsh Foxtail -0.22

Carex hirta Hairy Sedge 0.21 Bellis perennis Daisy -0.22

Molinia caerulea Purple Moor-grass 0.20 Senecio jacobaea Ragwort -0.20

� Figure 4.4: Change in plant species richness in 2m x 2m Targeted Plots in the Neutral Grassland Broad Habitat across Great Britain between 1990 and 2007. Signifi cant changes (*** p<0.001) are shown between the dates bracketed. 95% CI are shown for each data point.

0

2

4

6

8

10

12

14

16

18

Spe

cies

ric

hn

ess

(No.

of

spec

ies)

******

***

1990 1998 2007

� Figure 4.5: Change in the number of species of Farmland Bird Food Plants in 2m x 2m Targeted Plots in the Neutral Grassland Broad Habitat across Great Britain between 1990 and 2007. Signifi cant changes (** p<0.01, *** p<0.001) are shown between the dates bracketed. 95% CI are shown for each data point.

4

4.5

5

5.5

6

6.5

7

7.5

Nu

mbe

r of

spe

cies

****

***

01990 1998 2007

� Figure 4.6: Change in the number of species of Butterfl y Food Plants in 2m x 2m Targeted Plots in the Neutral Grassland Broad Habitat across Great Britain between 1990 and 2007. Signifi cant changes (** p<0.01, *** p<0.001) are shown between the dates bracketed. 95% CI are shown for each data point.

4

4.5

5

5.5

6

6.5

7

7.5 N

um

ber

of S

peci

es

*****

***

01990 1998 2007

� Flowering species of chalk grassland, England • © Sue Wallis

43


Great Britain between 1998 and 2007. This is supported by the list of plant species that decreased most, as they are predominantly species of short turf (Table 4.6). Wetter conditions are indicated by the increases in the mean Moisture Score (Table 4.4). These changes in character are illustrated by increases in frequency of species typically associated with wet meadows (Table 4.6).

The mean Fertility Score decreased in Main Plots (Table 4.4) but increased in Targeted Plots (Table 4.5) within Neutral Grassland in Great Britain between 1998 and 2007. The mean Ellenberg pH Score decreased signifi cantly in Main Plots across Great Britain between 1990 and 2007 (Table 4.4), with most of the decrease occurring between 1998 and 2007.

4.4.2 Changes in the Calcareous Grassland Broad Habitat

• The vegetation characteristics of Calcareous Grassland changed little between 1998 and 2007.

Species richness: There was a signifi cant increase in the plant species richness (1990 to 2007) and numbers of plant species used by butterfl y caterpillars as food (1990 to 1998) in the very small number of Main Plots in Calcareous Grassland (n=9) (Table 4.7).

There were no detectable changes in any of the other characteristics analysed between 1998 and 2007 and none in the Targeted Plots within Calcareous Grassland.

4.4.3 Changes in the Acid Grassland Broad Habitat

• Plant species richness decreased in Acid Grassland in Great Britain between 1998 and 2007.

• Competitive and moisture preferring plant species increased, while species of open ground decreased in Acid Grassland in Great Britain between 1998 and 2007.

� Table 4.7: Change in the characteristics of vegetation in 200m2 Main Plots in the Calcareous Grassland Broad Habitat across Great Britain between 1990 and 2007. Mean values for 1998 and 2007 are presented; those for 1990 are available in Annex 7. Arrows denote signifi cant change (p<0.05) in the direction shown. Grey columns with diagonal strikethrough denote insuffi cient data for analysis. Analyses are described in Box 1.3.

Mean values

(GB)


1998 – 2007


1990 - 1998


1990 - 2007


Species Richness (No. of Species) 41.1 43.0 ~

No. of Bird Food Species 14.6 14.1 ~

No. of Butterfl y Food Species 14.1 15.5 ~

Grass:Forb Ratio -0.67 -0.14 !

Competitor Score 2.02 2.21

Stress Tolerator Score 3.04 2.99

Ruderal Score 2.54 2.51

Light Score 7.19 7.13

Fertility Score 3.91 3.97

Ellenberg pH Score 6.07 6.03

Moisture Score 5.06 5.14

� Figure 4.7: Change in plant species richness in 200m2 Main Plots in the Acid Grassland Broad Habitat across Great Britain between 1990 and 2007. Signifi cant changes (** p<0.01, *** p<0.001) are shown between the dates bracketed. 95% CI are shown for each data point.

5

10

15

20

25

30

Spe

cies

ric

hn

ess

(No.

of

spec

ies)

0

*****

1990 1998 2007

44


Species richness: The plant species richness recorded in Main Plots in Acid Grassland increased in Great Britain between 1990 and 1998 and then decreased to 2007 (Table 4.8), so that there was no overall change (Fig. 4.7). The number of plant species used by farmland birds and butterfl y caterpillars as food followed the same pattern, the decrease in butterfl y food plant species being particularly noticeable in Scotland. This decrease was mirrored within areas of Acid Grassland targeted in CS for their botanical interest, with the exception of numbers of food plants for farmland birds (Table 4.9). Grasses became more dominant in these Targeted Plots between 1990 and 2007.

Other characteristics of vegetation in Acid Grassland: Competitive species increased signifi cantly in Main (Table 4.8) and Targeted Plots (Table 4.9) in Acid Grassland in Great Britain between 1998 and 2007 continuing the increase between 1990 and 1998. Stress tolerating species decreased in both Main and Targeted Plots across Great Britain between 1990 and 2007. Ruderal species increased signifi cantly in Great Britain between 1990 and 1998 in Main Plots then decreased signifi cantly between 1998 and 2007. The Fertility Score was unchanged in Acid Grassland in Main Plots in Great Britain between 1998 and 2007 but increased in Targeted Plots. Like other grasslands, the Moisture Score increased in Acid Grassland in Great Britain between 1998 and 2007. Amongst the list of plant species that increased most in frequency are several species characteristic of wet conditions e.g. Juncus squarrosus, Tricophorum cespitosum and Eriophorum angustifolium are all characteristic of very wet areas (Table 4.10). It is unclear why Carex nigra, C.pulicaris and C.viridula decreased as they also prefer wet conditions.

� Table 4.8: Change in the characteristics of vegetation in 200m2 Main Plots in the Acid Grassland Broad Habitat across Great Britain between 1990 and 2007. Mean values for 1998 and 2007 are presented; those for 1990 are available in Annex 7. Arrows denote signifi cant change (p<0.05) in the direction shown. Analyses are described in Box 1.3.

Mean values

(GB)


1998 – 2007


1990 - 1998


1990 - 2007


Species Richness (No. of Species) 21.6 19.6 ! ! ! ~ ~ ~

No. of Bird Food Species 5.6 5.2 ! ! ~ ~

No. of Butterfl y Food Species 9.2 8.4 ! ! ~ ~ ~

Grass:Forb Ratio 1.41 1.49 ~

Competitor Score 2.23 2.29 ~ ~ ~ ~ ~ ~

Stress Tolerator Score 3.42 3.40 ! !

Ruderal Score 1.87 1.83 ! ! ~

Light Score 6.90 6.91 ~ ~ ~ ~

Fertility Score 3.05 3.05 ~ ~

Ellenberg pH Score 3.72 3.75 ~

Moisture Score 6.24 6.30 ~ ~

� Acid grassland, Wales • © NERC

45


4.5 Priority Habitats of semi-natural grassland

4.5.1 Lowland Calcareous Grassland

In 1990 and 1998 the Calcareous Grassland Broad Habitat was recorded by surveyors and a digital altitude mask was used to diff erentiate between upland and lowland. In 2007 the emphasis on diff erentiating Lowland and Upland Calcareous Grassland was by botanical composition of the grasslands. The indicator species for Lowland Calcareous Grassland were Bromus erectus, Brachypodium pinnatum, Linum catharticum, Carlina vulgaris, Cirsium acaule, Hippocrepis comosa, Asperula cynanchica, Briza media, Koeleria macrantha and Helianthemum nummularia. The estimated area of Lowland Calcareous Grassland in Great Britain for 2007 was 45,000 ha (Table 4.11). The variance in the estimate refl ects the low representation of this nationally scarce and scattered Broad Habitat in CS (Annex 6).

� Table 4.10: The 10 plant species with the largest increase and decrease in frequency in Main Plots in the Acid Grassland Broad Habitat across Great Britain between 1998 and 2007.

� Table 4.11: Change in estimated area (‘000s ha) of Lowland Calcareous Grassland in Great Britain from 1998 to 2007. Arrows denote signifi cant change (p<0.05) in the direction shown.

Species with increasing frequency Change Index Species with decreasing frequency Change Index

Juncus squarrosus Heath Rush 0.26 Luzula campestris/multifl ora Woodrush -0.37

Holcus lanatus Yorkshire Fog 0.25 Carex pilulifera Pill Sedge -0.34

Trichophorum cespitosum Deergrass 0.24 Carex nigra Common Sedge -0.28

Urtica dioica Stinging Nettle 0.23 Poa annua Annual Meadow- grass -0.27

Empetrum nigrum Crowberry 0.23 Agrostis capilliaris Common Bent -0.26

Trifolium repens White Clover 0.22 Juncus bulbosus Bulbous Sedge -0.24

Senecio jacobaea Ragwort 0.20 Carex pulicaris Flea Sedge -0.24

Ranunculus acris Meadow Buttercup 0.20 Festuca ovina agg. Sheep’s Fescue -0.24

Eriophorum angustifolium Common Cotton-grass 0.20 Carex viridula ssp Yellow Sedge -0.24

Cirsium arvense Creeping Thistle 0.19 Bellis perennis Daisy -0.19

Lowland Calcareous Grassland

1998Area

(‘000s ha)

2007Area

(‘000s ha)

Direction of signifi cant

changes 1998-2007

GB 47.4 44.5

England 30.7 28.5

Scotland 16.4 15.8

Wales 0.3 0.2

� Table 4.9: Change in the characteristics of vegetation in 2m x 2m Targeted Plots in the Acid Grassland Broad Habitat across Great Britain between 1990 and 2007. Mean values for 1998 and 2007 are presented; those for 1990 are available in Annex 7. Arrows denote signifi cant change (p<0.05) in the direction shown. Analyses are described in Box 1.3.

Mean values

(GB)


1998 – 2007


1990 - 1998


1990 - 2007


Species Richness (No. of Species) 13.8 12.3 ! ! ! ~ !

No. of Bird Food Species 3.4 3.3 ~

No. of Butterfl y Food Species 5.8 5.4 ! !

Grass:Forb Ratio 1.33 1.41 ~ ~ ~ ~ ~

Competitor Score 2.27 2.35 ~ ~ ~ ~ ~ ~

Stress Tolerator Score 3.42 3.34 ! ! ! ! !

Ruderal Score 1.90 1.91

Light Score 6.96 6.93 ! ~ ~ ~ ~

Fertility Score 3.03 3.12 ~ ~ ~

Ellenberg pH Score 3.90 3.92

Moisture Score 6.39 6.39

46


4.5.2 Upland Calcareous Grassland

As with Lowland Calcareous Grassland, Upland Calcareous Grassland was identifi ed in 1998 using a digital altitudinal mask. In 2007, Upland Calcareous Grassland was identifi ed by the botanical indicators Sesleria albicans, Thymus praecox and Galium sterneri. Montane forms sometimes contain Arctic-Alpine plants, such as Alchemilla alpina, Polygonum viviparum, Dryas octopetala and Silene acaulis. The area estimate for Great Britain in 2007 was 19,000 ha, a decrease between 1998 and 2007 (Table 4.12). There is high variance in the estimates for this Priority Habitat because it is so scarce (Annex 6). Most of this Priority Habitat is found in a few large well known sites that are not within the CS sample.

4.6 Changes to the soils (0-15cm) of semi-natural grasslands

• The mean pH of Neutral Grassland soils (0-15cm) increased signifi cantly in Great Britain between 1998 and 2007, but the mean pH of Acid Grassland soils (0-15cm) did not change signifi cantly in Great Britain between 1998 and 2007.

• There was no signifi cant change in the mean carbon concentration in Neutral Grassland soils (0-15cm) in Great Britain between 1998 and 2007, but in Acid Grassland soils (0-15cm) there was a signifi cant decrease in Great Britain during the same period.

4.6.1 Neutral Grasslands

Soil (0-15cm) pH: The mean pH of soil (0-15cm) samples in Main Plots within Neutral Grassland in Great Britain increased signifi cantly between 1998 and 2007, from pH 6.00 to 6.14. Earlier increases in pH between 1978 and 1998 and overall from 1978 to 2007 were also signifi cant (Table 2.8, Fig 4.8). The mean Ellenberg pH Score of the vegetation (Table 4.4) did not change consistently with the soil pH.

Soil (0-15cm) carbon concentration: There was no signifi cant change in the carbon concentration of soil (0-15cm), approximately 62 g/kg, in Neutral Grassland in Great Britain between 1998 and 2007 or between 1978 and1998 or between 1978 and 2007 (Table 2.8).

Bulk density and soil (0-15cm) carbon stock: The mean bulk density of Neutral Grassland soils (0-15cm) in Great Britain was 0.9 g/cm3 (in the top 15cm) which when combined with mean soil (0-15cm) carbon concentration indicated a soil (0-15cm) carbon stock of 62 t/ha (Table 2.9).

4.6.2 Calcareous Grasslands

An insuffi cient number of soil samples were taken from the Calcareous Grassland Main Plots for a statistical analysis to be undertaken for this Broad Habitat.

4.6.3 Acid Grasslands

Soil (0-15cm) pH: There was no signifi cant change in the mean pH of soil (0-15cm) samples in the Main Plots within Acid Grasslands in Great Britain, between 1998 and 2007 (Table 2.8, Fig. 4.9). This contrasts with the signifi cant increase from pH 4.43 in 1978 to pH 4.72 in 1998, which also largely accounts for the signifi cant increase in soil (0-15cm) pH between 1978 and 2007.

Soil (0-15cm) carbon concentration: There was a signifi cant decrease in the mean carbon concentration of soil (0-15cm) in Acid Grasslands for Great Britain between 1998 and 2007 (Table 2.8), whereas there was no signifi cant change between 1978 and 1998. A signifi cant decrease in soil (0-15cm) carbon concentration was also observed between 1998 and 2007 in the relatively carbon-rich Acid Grassland soils in Scotland, but there were no signifi cant changes in England and Wales.

Bulk density and soil (0-15cm) carbon stock: The mean bulk density of Acid Grassland soils (0-15cm) in Great Britain was 0.4 g/cm3 which, when combined with mean soil (0-15cm) carbon concentration indicated a soil (0-15cm) carbon stock of 82 t/ha (Table 2.9).

� Figure 4.8: The change in mean pH of soils (0-15cm) from Neutral Grasslands in Great Britain between 1978 and 2007. Signifi cant changes (* p<0.05, *** p<0.001) are shown between the dates bracketed. 95% CI are shown for each data point.

3.003.504.004.505.005.506.006.507.007.508.00

pH

***

***

*

1978 1998 2007� Table 4.12: Change in estimated area (‘000s ha) of Upland Calcareous Grassland in Great Britain from 1998 to 2007. Arrows denote signifi cant change (p<0.05) in the direction shown.

Upland Calcareous Grassland

1998Area

(‘000s ha)

2007Area

(‘000s ha)


1998-2007

GB 21.47 18.89 !

England 1.99 0.59

Scotland 19.24 18.05

Wales 0.15 0.15

47


4.7 Discussion and conclusions

4.7.1 Neutral Grassland

The area of the Neutral Grassland Broad Habitat was 2.4 million ha in 2007, 10% of the land area of the UK, and two thirds of this was found in England. The area of Neutral Grassland increased in Great Britain by 30% between 1990 and 2007. Neutral Grassland is a dynamic habitat with proportionately high conversions to and from other Broad Habitats. Between 1998 and 2007, Neutral Grassland gained mostly at the expense of Arable and Horticulture and Coniferous Woodland Broad Habitats.

Between 1998 and 2007, in the 200m2 Main Plots that represented widespread examples of Neutral Grassland, reductions in plant species richness (including food plants of farmland birds and butterfl y caterpillars) were detected only in Scotland. However, in areas targeted in CS for their botanical diversity (Targeted Plots), the plant Species Richness Score decreased by 9.8% between 1998 and 2007 in Great Britain, and 13% between 1990 and 2007. These losses in plant species richness were associated with a shift towards more competitive, shade tolerant and nutrient demanding plants, with a decrease in ruderal species. This suggests a successional change in these more diverse patches within the Neutral Grassland Broad Habitat.

It is not yet clear why the decrease in Fertility Score occurred in Main Plots in Neutral Grassland, as many of the more competitive, shade tolerant species are also those that prefer fertile conditions. Both atmospheric nitrogen deposition and sheep grazing intensity have been previously linked weakly with an increase in Fertility Score within semi-natural grassland in Great Britain between 1978 and 1998, but a clear signal of nutrient overload (eutrophication) was not detected between 1998 and 2007 in Neutral Grasslands. This apparent stability coincided with a period during which atmospheric nitrogen deposition remained relatively stable but cattle and sheep numbers decreased.

The signifi cant increase in mean Fertility Score in the Targeted Plots in Neutral Grassland between 1990 and 2007 is more understandable. It indicates a clear shift toward more nutrient-

demanding species but the reduction in mean Light Score and increase in mean Competitor Score also indicate greater shade and taller vegetation. These plots tend to sample small patches of agriculturally marginal but botanically more interesting vegetation embedded in intensive farmland. So, when fi rst recorded in 1990, they started relatively richer in species more typical of low fertility but have been subsequently aff ected by lack of management and exposure to nutrient surpluses from nearby sources. This is a somewhat diff erent picture from that seen in the Main Plots in the Neutral Grassland Broad Habitat, where the Fertility Score actually decreased across Great Britain between 1998 and 2007.

Soils (0-15cm) in Neutral Grassland became increasingly neutral (5.5 to 6.1 pH) between 1978 and 1998, and between 1998 and 2007.

4.7.2 Calcareous Grassland

Calcareous Grassland has a limited extent compared to other semi-natural and improved grassland types in the UK and is consequently relatively poorly represented in the CS sample. The estimated area of Calcareous Grassland in 2007 was 59,000 ha, well under 1% of the land area of the UK. Between 1990 and 2007, the area of

� Figure 4.9: The change in pH of soils from Acid Grasslands in Great Britain between 1978 and 2007. Signifi cant changes (** p<0.01, *** p<0.001) are shown between the dates bracketed. 95% CI are shown for each data point.

3.003.504.004.505.005.506.006.507.007.508.00

pH

******

1978 1998 2007

� Species rich meadow, England • © Sue Wallis

48


Calcareous Grassland in Great Britain decreased by 27% but most of this (22%) occurred in the period 1990 to 1998.

In the more extensive areas of Calcareous Grassland (Main Plots) a small increase (17%) in plant Species Richness Score was detected in Great Britain between 1990 and 2007 and no change was detected between 1998 and 2007. In more fragmented examples of Calcareous Grassland, and of other habitats within Calcareous Grassland represented by Targeted Plots there was no signifi cant change in plant species richness between 1990 and 2007. However, there were increases in the number of plant species used by butterfl y caterpillars as food between 1998 and 2007, associated with increases in competitive and nutrient demanding species.

A large proportion of the Calcareous Grassland of Great Britain is now under conservation management and/or protection. The reduction in the rate of loss and also the lack of changes in vegetation characteristics suggest that interventions are beginning to be eff ective.

4.7.3 Acid Grassland

In 2007, Acid Grassland had a total estimated cover of 1.6 million ha, about 6.5% of the land area of the UK. Most of this grassland (62%) occurs in Scotland. Between 1990 and 2007 the area of Acid Grassland fell by 13%, but the decrease was greater between 1990 and 1998 and there was a substantial increase in area between 1998 and 2007 in the uplands of Scotland and Wales. Acid Grassland is a relatively stable Broad Habitat with small conversions between similar Broad Habitat types, and particularly Bracken.

Plots within extensive areas of Acid Grassland (Main Plots) exhibited contrasting trends in plant species richness, with increases between 1990 and 1998 followed by decreases between 1998 and 2007. However, despite these contrasts in plant species richness there were consistent trends towards more competitive and plant species casting or preferring shade (generally taller plants). Similar trends were observed in areas targeted in CS for their botanical diversity (Targeted Plots) but there was also a decrease in stress tolerating species and an increase in nutrient-demanding species.

Reasons for the changes in Acid Grassland require further investigation, but the increases in competetive species and taller plant species would be consistent with the eff ects of reduced grazing pressure, related to decreases in the numbers of sheep and cattle over the same period.

4.7.4 Semi-natural grasslands as a whole

The signifi cant continued loss of plant species richness in areas targeted in CS for their botanical interest within semi-natural grasslands could be related to less intensive management. Reduced stocking rates and cutting, would, when combined with wetter conditions and higher soil pH, lead to the changes in vegetation characteristics that were observed. Taller, more competitive species increased, suppressing smaller species and subsequently reducing species richness.

The increase in the area of Semi-Natural Grasslands between 1998 and 2007 might not be permanent. Whilst the area of Calcareous Grassland is now likely to remain more stable because of conservation intervention, much of the new Neutral Grassland could be ploughed again or reforested. The area of Acid Grassland varies over time because of the transitional nature of the plant communities at the boundaries between Acid Grassland, Bracken and Dwarf Shrub Heath Broad Habitats. A larger eff ect may be caused by changes in the livestock density in the uplands, along with management to remove bracken and positive conservation management of Dwarf Shrub Heath.

� Mixed upland grass, N Ireland • © Mark Wright

49


Contacts

For further information on Countryside Survey see www.countrysidesurvey.org.uk or contact: Countryside Survey Project Offi ce, Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP

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The Countryside Survey partnership has endeavoured to ensure that the results presented in this report are quality assured and accurate. Data has been collected to estimate the stock, change, extent and/or quality of the reported parameters. However, the complex nature of the experimental design means that results can not necessarily be extrapolated and/or interpolated beyond their intended use without reference to the original data.

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